The present invention relates to swage type fasteners including a pin having a plurality of combination locking and breakneck grooves and a collar adapted to be swaged into the grooves with one of the grooves acting as a breakneck whereby the excess length of pin is severed generally at the end of the collar and also relates to a method of making the pin.
The present invention relates to multigrip fasteners of the type shown in U.S. Pat. Nos. 4,208,943 and 4,342,529 and the disclosures of those patents are incorporated herein by reference.
As seen from the noted patents, fasteners of the multigrip type include a pin having combination locking and breakneck grooves and a collar adapted to be swaged into these grooves. The contour of the grooves are such that any one of the grooves when located at the end of the collar can function as a breakneck. It has been found, however, that with pins made of ferrous materials inconsistent breaks can occur caused by variations in the material and/or its processing. Thus if the material is too brittle breaks may occur several grooves outside of the collar or the collar may not completely swage before the pin fractures. On the other hand, the material as processed may have a microstructure permitting excessive stretching before fracture resulting in breaks within the collar and/or breaks across more than one groove.
In the present invention, the multigrip pin is formed generally into its final shape and then is subject to a heat treating process to provide a desirable microstructure whereby more consistent breaks at the selected groove occurs.
In one form of the invention a desirable microstructure consists of predominantly pearlite colonies with a proeutectoid ferrite matrix interspersed at the boundaries of pearlite colonies. The amount and thickness of the proeutectoid ferrite can be controlled to produce the desired ductility of the pin. It has been found that the lesser amount of proeutectoid ferrite inherent in coarse grained steel is more advantageous to the function of the pin. The size of the pearlite colonies (or the apparent austenitic grain size) is generally coarser than ASTM 5 and generally within a range of from about ASTM 1 to about ASTM 5.
Therefore it is an object of the present invention to provide a process for making a multigrip pin having a microstructure which enhances the consistency of fracture at the desired one of the combination locking and breakneck grooves.
It is a further object of the present invention to provide a process for making a multigrip pin of a ferrous material having a microstructure comprised predominantly of coarse grained pearlite colonies with controlled amounts of proeutectoid ferrite interspersed at the pearlite colony grain boundaries.
It is another object of the present invention to provide a multigrip pin manufactured by the process of the present invention.
It is still another object of the present invention to provide a multigrip pin having a grain structure comprised predominantly of coarse grained pearlite colonies and controlled amounts of proeutectoid ferrite interspersed at the pearlite colony grain boundaries as manufactured by the process of the present invention.
Other objects, features, and advantages of the present invention will become apparent from the subsequent description and the appended claims, taken in conjunction with the accompanying drawings in which: